The invention is generally directed to a composition having antimicrobial activity, including activity against microbial spores. More particularly, a composition of the invention includes hydrogen peroxide, a carboxylic acid, and a peroxycarboxylic acid and has a weight ratio of a peroxycarboxylic acid to hydrogen peroxide of at least 4:1. A composition of the invention is particularly useful for microbiocidal treatment of substances being contaminated with microorganisms of the Bacillus cereus group.
A variety of industries such as, for example, the food industry, health-care industry, institutional industry, and hospitality industry, have a need to use antimicrobial treatments to reduce microbial populations in the environments in which these industries are carried out. In some instances, these antimicrobial treatments include the use of peracid materials.
Compositions for peracid materials and their use for reducing microbial populations are known. For example, Grosse-Bowing et al. (U.S. Pat. Nos. 4,501,058 and 4,501,059) and Oakes et al. (U.S. Pat. Nos. 5,200,189; 5,314,687; and 5,718,910) disclose peracid materials in a variety of end uses. Similarly, Cosentino et al. (U.S. Pat. No. 5,279,735) teach the use of peracid materials as a sterilant for hollow fiber membranes such as those used in kidney-dialysis procedures. Richter et al. (U.S. Pat. No. 5,436,008) teach unique peracid sanitizing materials having applicability for treating food-processing equipment.
Typical peracid materials include an equilibrium mixture of acetic acid, hydrogen peroxide, peroxyacetic acid, and a stabilizer. A stabilizer typically reduces the impact of divalent or trivalent metal ions on the decomposition of the active peroxygen species. Suitable stabilizers include a chelant or sequestrant.
Although peracid materials typically have a broad spectrum of antimicrobial properties, their activity against bacterial spores, fungal spores, and fungi can be less than desirable. Killing, inactivating, or otherwise reducing the active population of bacterial spores, fungal spores, and fungi on surfaces (e.g., especially food surfaces and food-contact surfaces, which are typically hard surfaces including metal, glass, composite materials, etc.) is a particularly difficult problem. In particular, bacterial spores have a unique chemical composition of spore layers that make them more resistant than vegetative bacteria to the antimicrobial effects of chemical and physical agents. Like bacterial spores, the unique chemical composition of fungal cells, especially mold spores, makes them more resistant to chemical and physical agents than other microorganisms.
A particularly difficult problem relates to microbiocidal treatment of bacterial spore-forming microorganisms of the Bacillus cereus group. Microorganisms of the Bacillus cereus group include Bacillus cereus, Bacillus mycoides, Bacillus anthracis, and Bacillus thuringiensis. These microorganisms share many phenotypical properties, have a high level of chromosomal sequence similarity, and are known enterotoxin producers.
Although all spore-forming microorganisms are problematic for microbiocidal treatments because they form spores, Bacillus cereus is one of the most problematic because Bacillus cereus has been identified as possessing increased resistance to germicidal chemicals used to decontaninate environmental surfaces. (See, e.g., Blakistone et al., Efficacy of Oxonia(copyright) Active Against Selected Sporeformers, Journal of Food Protection, Volume 62, pp. 262-267, reporting that Bacillus cereus was more tolerant to the effects of peroxyacetic acid germicides formulated using conventional parameters than all other spore-forming bacteria tested, including other Bacillus and Clostridium species.).
Bacillus cereus is a particularly well-established enterotoxin producer and food-borne pathogen. This organism is frequently diagnosed as a cause of gastrointestinal disorders and has been suggested to be the cause of several food-borne illness outbreaks. The organism is ubiquitous in nature, and as a consequence, is present in animal feed and fodder. Due to its rapid sporulating capacity, the organism easily survives in the environment and can survive intestinal passage in cows. The organism can contaminate raw milk via feces and soil, and Bacillus cereus can easily survive the pasteurization process.
Bacillus cereus is also known to cause serious human illness via environmental contamination. For example, Bacillus cereus is known to cause post-traumatic eye infections, which can cause visual impairment or loss of vision within 12-48 hours after infection.
A substantial need therefore exists for improving peracid materials so that they have greater antimicrobial activity toward bacterial spores and fungi and other microorganisms with resistance to germicidal materials, particularly activity against microorganisms of the Bacillus cereus group.
A common belief in the field of microbiocidal treatments is that peroxycarboxylic acid and hydrogen peroxide work cooperatively in microbiocidal treatments to reduce microbial populations. And it is generally believed that peroxyacetic acid and hydrogen peroxide at aqueous concentrations of about 1 to 10 weight percent can each have significant independent antimicrobial properties.
Yet according to this invention, hydrogen peroxide has surprisingly been found to facilitate the resistance of bacterial spores, particularly of the Bacillus cereus group, toward peracid material. Means to reduce peroxide induced resistance and increase efficacy is needed.
A composition of the invention is directed to reducing the concentration of hydrogen peroxide relative to a peroxycarboxylic acid from conventional concentrations to a level described herein. Reducing the hydrogen peroxide concentration relative to peroxycarboxylic acid provides a degree of antimicrobial properties that is surprising and unique in this technology.
A composition of the invention typically includes hydrogen peroxide, a carboxylic acid, and a peroxycarboxylic acid in which the ratio of peroxycarboxylic acid to hydrogen peroxide is at least 4:1, preferably at least 5:1, more preferably at least 6:1, and even more preferably at least 7:1. These ratios are expressed in parts by weight of peroxycarboxylic acid to each part by weight of hydrogen peroxide.
A composition of the invention typically has increased antimicrobial activity, particularly antisporicidal activity, as compared to peracid materials containing greater amounts of hydrogen peroxide relative to a peroxycarboxylic acid than a composition of the invention, when all conditions except for the hydrogen-peroxide amount are held constant.
In one embodiment, a concentrate composition includes hydrogen peroxide in an amount of between about 0.5 weight percent and about 80 weight percent; a carboxylic acid of the formula R(COOH)n, in which R includes hydrogen, alkyl, alkenyl, alicyclic group, aryl, heteroaryl, or heterocyclic group, and n is 1, 2, or 3, the carboxylic acid being present in an amount of between about 5 weight percent and about 80 weight percent; and a peroxycarboxylic acid of the formula R(COOOH)n, in which R includes hydrogen, alkyl, alkenyl, alicyclic group, aryl, heteroaryl, or heterocyclic group, and n is 1, 2, or 3, the peroxycarboxylic acid being present in an amount of between about 0.2 weight percent and about 30 weight percent, and the ratio of the peroxycarboxylic acid to hydrogen peroxide is at least 4:1.
In another embodiment, a use-solution composition includes hydrogen peroxide in an amount of up to 2500 ppm; a carboxylic acid of the formula R(COOH)n, in which R includes hydrogen, alkyl, alkenyl, alicyclic group, aryl, heteroaryl, or heterocyclic group, and n is 1, 2, or 3, the carboxylic acid being present in an amount of between about 2 ppm and about 27000 ppm; and a peroxycarboxylic acid of the formula R(COOOH)n, in which R includes hydrogen, alkyl, alkenyl, alicyclic group, aryl, heteroaryl, or heterocyclic group, and n is 1, 2, or 3, the peroxycarboxylic acid being present in an amount of between about 1 ppm and about 10000 ppm, and the ratio of the peroxycarboxylic acid to hydrogen peroxide is at least 4:1.
A composition of the invention can also contain additives such as, for example, a quaternary ammonium compound, a stabilizing agent, a hydrotrope, a surfactant, and/or another adjuvant to provide additional properties.
In one embodiment, a composition of the invention further includes a quaternary ammonium compound. In some instances, the sporicidal and fungicidal efficacy of a composition of the invention can be further improved by including a quaternary compound.
A method of the invention typically include contacting a substance with a composition of the invention to reduce microbial populations. This method is surprisingly effective for killing bacterial spores, particularly spore of the Bacillus cereus group.
In one embodiment, a method includes contacting a substance being contaminated with microorganisms of the Bacillus cereus group with a composition including a peroxycarboxylic acid and hydrogen peroxide in a ratio of a peroxycarboxylic acid to hydrogen peroxide of about 4:1 or greater, preferably about 5:1 or greater, more preferably about 6:1 or greater, and even more preferably about 7:1 or greater.
Another method of the invention is directed to desirably reducing the concentration of hydrogen peroxide relative to the concentration of a peroxycarboxylic acid in a composition of the invention by, for example, reaction with a catalytic surface, reaction with a chemical agent, or application of other chemical techniques.
In one embodiment, the concentration can be desirably reduced relative to the concentration of a peroxycarboxylic acid by controlling the equilibrium reaction between hydrogen peroxide and a carboxylic acid.
In another embodiment, the concentration can be desirably reduced relative to the concentration of a peroxycarboxylic acid by exposing a composition of the invention to a hydrogen peroxide-destroying agent such as catalase.